The present invention relates to a display device for displaying a plurality of images of different signal sources on one screen.
Generally, a conventional display device has only one circuit as a signal line driving circuit and only one circuit as a gate line scanning circuit. Accordingly, video signals of all formats (for example, a picture signal of a photograph or the like requiring high definition and a picture signal of a portable device standby screen for which low definition is good enough) are displayed by operation of the same circuits and accordingly power consumption scarcely changes.
Recently, considering this problem, is proposed a display device that can drive signal lines according to various demands and can display a plurality of picture data in superposition without previously synthesizing them, and also is proposed an electronic device using such a display device.
US2002/0075249(JP-A-2002-32048) describes a picture display device provided with a plurality of data signal line driving circuits of respective different configurations and a plurality of scanning signal line driving circuits of respective different configurations. Each data signal line driving circuit or scanning line driving circuit can display a picture of a different format from the others. By switching a driving circuit to operate, depending on types of images to be inputted or use environment, it is possible to realize display according to the optimum display format and to reduce power consumption. Further, overwriting of pictures can be realized when a plurality of driving circuits are used to write respective video signals into signal lines being delayed from each other. Thus, it is possible to display a plurality of pictures in superposition, without externally processing video signals.
However, it is difficult for the technique disclosed in US2002/0075249(JP-A-2002-32048) to arbitrarily control superposition (overwriting) of images on one horizontal line. Further, to synthesize and display two signals having different frame rates, it is necessary to synchronize those two signals, and it becomes a burden on external systems (systems for outputting a video signal and a picture signal).